A tool chucking device has already been described in which the coupling head contains several radially movable locking balls. For coupling the tool with the draw-in bar these balls are forced into special recesses in the tool shank and create a positive coupling connection between the coupling head and the tool shank (Wotan-Werke GmbH, Dusseldorf, prospectus No. 8358/3.0/5.72, page 4). It is a drawback of this known arrangement that the surface available for transmitting the tensile forces from the coupling head to the tool shank is very restricted because of the limited number and size of the locking balls and, particularly in the case of larger sized devices, an optimum holidng force cannot be obtained because it would involve exceeding the maximum permissible surface loading. An increase in the number of locking balls or of their dimensions is usually impossible because the space available inside the tool spindle is restricted by other factors. Another drawback of the known device is that its production and assembly is costly owing to the many individual components which it comprises.
It is an object of the present invention to provide a tool chucking device of the above-specified kind which combines simplicity and compactness with the ability to provide a very considerable holding respectively clamping force.
In one embodiment of the invention, this object is achieved by contriving the coupling head in the form of a slotted resiliently expandable sleeve-like member or the like having an internal grooved profile adapted to engage a matching external grooved profile on the tool shank, and by providing means for expanding the slotted sleeve-like member during its displacement in ejecting direction for the purpose of receiving or releasing the tool shank.
The slotted sleeve-like member is structurally as well as functionally a very simple component. The grooved profile provides a relatively large load-transferring surface for transmitting the holding or tightening force since this surface may extend around the entire circumference of the coupling head and tool shank without being restricted to a number of locking balls. More particularly, the invention permits a plurality of grooves to be provided axially in succession and the load transferring surface to be thereby increased nearly as many times as may be desired. According to the invention the grooved profile may be a screw thread or it may consist of a plurality of annular grooves or collars arranged in axial succession.
Since a plurality of axially consecutive bearing surfaces can be provided, the radial dimensions of each individual surface may be small and the slotted sleeve-like member will not thus have to be significantly deformed.
Another advantage is considered to reside in that the proposed device also permits tools to be chucked up which are provided with conventional screw threads, provided the coupling head is provided with the complementary matching threads. This fact enables the large numbers of spare conventional tools still held in stock by many users to be used up as desired.
Besides the said embodiment in which the gooved profile of the coupling head is arranged to engage the outside of a tool shaft provided with a complementary grooved profile, the scope of the invention is also intended to comprise the converse arrangement in which the slotted sleeve-like member has an external grooved profile for engagement with a corresponding internal gooved profile in an axial bore in the end of the tool shank.
The elastic deformation of the slotted sleeve-like member which enables the sleeve-like member to engage and release the tool is produced by cam elements located inside the tool spindle, such as pins projecting radially inwards or sleeves surrounding the slotted sleeve-like member. The pins or sleeves are provided with cam faces which cooperate with cam faces on the slotted sleeve-like member and cause the desired deformation when the sleeve-like member is axially displaced.
The cam elements are so designed that the draw-in movement and the ejecting movement of the locking head are each divided into two stages. In the first stage of the operation of drawing-in the tool, the slotted sleeve-like member is arranged to engage the tool shank; in the second stage, the coupling head performs the axial draw-in movement.
In the first stage of the ejecting operation, the tool is initially still retained by the coupling head to permit the force needed for releasing the tool from the spindle socket to be applied to the tool. During the second stage of the ejecting motion, the slotted sleeve-like member is deformed to release the tool from the coupling.
When a tool is inserted there is, however, some risk of the grooved profiles facing each other crest-to crest, so that mutual engagement cannot take place. In order to prevent the device from being thus jammed, the cam elements are so designed that in the first stage of the draw-in motion they are able to yield against a spring load by an amount corresponding roughly to the axial pitch of the grooves, thus enabling the locking head to shift in relation to the tool shank until mutual engagement is possible. Not until this is the case will the cam elements provide rigid counterfaces for the cam faces on the slotted sleeve-like member and thus in the second stage of the draw-in motion produce the required deformation of the sleeve-like member for engaging the tool.
In order to ensure that the tool is reliably ejected, steps must be taken to ensure that the first stage of the ejecting motion, which is the inversion of the second stage of the draw-in motion, is sufficiently large. According to the invention, a spring stop for the tool shank is therefore provided which intercepts the tool when it is initially inserted into the spindle socket and which prevents it from making immediate contact with the socket walls before it is actually forced into contact with them by the pull of the draw-in bar.
Other features of the invention will become apparent from further appendant claims and from the following particular description of embodiments of the invention.